Recently, in particular in vehicle-mounted power circuit devices, higher output and size/weight reduction have been strongly demanded, and thus heat generation density of electronic components mounted in a power device is increasing. In addition, safety is also highly demanded in the vehicle-mounted power circuit devices. Accordingly, in some cases, for semiconductor elements which account for a large proportion of the cost of a vehicle-mounted power circuit device and whose failure leads to immediate stop of a vehicle, an overheat protection control device is mounted for the purpose of utilizing the performance of the semiconductor elements to the maximum and for the purpose of preventing a failure of the vehicle.
In a conventional overheat protection control device for semiconductor elements, a temperature sensor is arranged on each semiconductor element to measure the temperature of the semiconductor element, and overheat protection is applied by limiting an output such that the semiconductor element is not damaged. Applying overheat protection expands a temperature region in which the semiconductor element is used, improves the performance of the circuit device, and prevents a failure of the semiconductor element.
When the circuit device includes multiple semiconductor elements, the temperatures of the multiple semiconductor elements should be monitored. Accordingly, there has been proposed a device in which signals from temperature sensors are integrated via an input/output interface to reduce the number of input ports of a microcomputer with respect to the number of semiconductor elements and to downsize a temperature detection device (for example, PTD 1). In addition, there has been proposed a method of determining loss from a control command value and estimating the temperature of a semiconductor element using a predetermined thermal circuit network (for example, PTD 2).